In recent years, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. In addition, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery module having a plurality of battery cells electrically connected to each other because high output and large capacity are necessary for the middle or large-sized devices.
Preferably, the middle or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle or large-sized battery module. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing cost of the pouch-shaped battery is low, and it is easy to modify the shape of the pouch-shaped battery.
Battery cells constituting the middle or large-sized battery module may be secondary batteries which can be charged and discharged. Consequently, a larger amount of heat is generated from such high-output, large-capacity secondary batteries during charge and discharge of the secondary batteries. In particular, the laminate sheet of each pouch-shaped battery widely used in the battery module has a polymer material exhibiting low thermal conductivity coated on the surface thereof with the result that it is difficult to effectively lower overall temperature of the battery cells.
If the heat, generated from the battery module during charge and discharge of the battery module, is not effectively removed from the battery module, the heat accumulates in the battery module with the result that deterioration of the battery module is accelerated. According to circumstances, the battery module may catch fire or explode. For this reason, a middle or large-sized battery pack for vehicles, which is a high-output, large-capacity battery including a plurality of middle or large-sized battery modules, needs a cooling system to cool battery cells mounted therein.
Each battery module mounted in the middle or large-sized battery pack is generally manufactured by stacking a plurality of battery cells with high integration. In this case, the battery cells are stacked in a state in which the battery cells are arranged at predetermined intervals such that heat generated from the battery cells during charge and discharge of the battery cells can be removed. For example, the battery cells may be sequentially stacked in a state in which the battery cells are arranged at predetermined intervals without using an additional member. Alternatively, in a case in which the battery cells have low mechanical strength, one or more battery cells may be mounted in a cartridge to constitute a unit module, and then a plurality of unit modules may be stacked to constitute a battery module. In a case in which the cartridge is used, the mechanical strength of the battery cells is improved; however, the overall size of the battery module is increased.
In addition, coolant channels are defined between the stacked battery cells or between the stacked battery modules such that heat accumulated between the stacked battery cells or between the stacked battery modules can be effectively removed.
Particularly, in a case in which the cooling structure is a water-cooled type cooling structure, a plurality of coolant channels is defined between the battery cells or between the battery modules with the result that it is very difficult to design the cooling structure. In addition, in a case in which a cooling member or a heat conduction member is mounted at a specific region of the battery pack to configure the cooling structure, the overall size of the battery pack is increased.